props: tractor v pusher, q tip, ducted?

If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling. The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects. Finally, does anyone know of any work on small airplanes
using a ducted prop (shrouding it rather than using the q tip bent
end? I'm not worried about ease of flying (the problem with pusher
props are pretty obvious) but rather with converting the horsepower
delivered to the prop into usable thrust, that is, getting the
greatest efficiency (miles per gallon is a crude way of expressing it)
for a small single.

opps, should have said Cessna 337.

On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

Kingfish wrote:
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?


I believe the performance is better flying on the rear engine alone vs.
the front alone.

Matt

"Kingfish" wrote in message
oups.com...
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

The single engine climb performance is pitiful regardless of which engine is
caged, but the aircraft has more performance on the back engine than the
front. That may or may not be due to prop efficiency. It could also be due
to reduced fuselage drag. The tractor prop blows a high speed stream of air
across the fuselage, creating its own source of drag. This isn't as much of
a factor with the pusher.

KB

The data I saw showed the 337 single engine pusher doing better, maybe
it is old data. The tractor prop is wasting energy blowing on the
windscreen and cowling, problems the pusher doesn't have. I know the
biggest gains the Mooney Exec had in going to the 201 had was because
of the cowling and windscreen redesign.

I never heard that q tips did worse than straight bladed props, that
was an interesting observation.

Aren't Lakers configured as pushers? That is an interesting example.
because the engine is just hanging out there, you could put the prop
on either end.

Tina wrote in news:1186370891.595213.170320
@w3g2000hsg.googlegroups.com:

The data I saw showed the 337 single engine pusher doing better, maybe
it is old data. The tractor prop is wasting energy blowing on the
windscreen and cowling, problems the pusher doesn't have. I know the
biggest gains the Mooney Exec had in going to the 201 had was because
of the cowling and windscreen redesign.


That's for the early airplanes regarding the Skymasters. the loss was in
cooling drag, which Cessna improved. After that the SE ceiling cruise
and climb were virtually identical, but the reputation the rear engine
had for better SE performance never went away..

I never heard that q tips did worse than straight bladed props, that
was an interesting observation.


Actaully, it was more than an observation. the Q tips were installed as
a noise requirement for Swiss registered airplanes. These airplanes had
a supplememt to the POH with degraded performance. Having said that they
also had "Swiss Mufflers" but they're supposed to have no effect on
performance.
Also flew a couple of Arrows similarly equipped as well as a Cessna 182
RG. Same deal for all of them IIRC. Some were German and I seem to
remember they had a different muffler assembly in Germany which deliverd
worse performance and made more noise.


Aren't Lakers configured as pushers? That is an interesting example.
because the engine is just hanging out there, you could put the prop
on either end.


Well, you're getting down to comparing apples with oranges. You'd have
to take two essentially identical aircraft and try both configurations
with it for a satisfacory answer based solely on observed performance,
but in reality, a real world airplane is going to throw so many other
variables, such as cooliing requirements, planform due to CG
considerations, disc availability due to fuselage cross section, whoch,
of course is down to cabin space, mission requirements yadda yadda
yadda. At the end of the day, when you look at similarly powered
aircraft with similar missions, or even better, if you look at the Cafe
racers, the evidence says it's al down to how clever the designer is,
and there's not a lot in any configuration, pusher, tractor tandem wing,
canard or conventional...



Bertie

On Aug 5, 11:46 pm, Bertie the Bunyip wrote:

That's for the early airplanes regarding the Skymasters. the loss was in
cooling drag, which Cessna improved. After that the SE ceiling cruise
and climb were virtually identical, but the reputation the rear engine
had for better SE performance never went away..


How can that be? The engine cowling has the same openings wether the
engine is turning or not. In other words, whatever the drag of the
front engine cowling, it should be the same whether the engine is
turning or not.

I'm assuming that the propeller does not effect airflow tooooo much
near the root, where it spins slowly and has a less aerodynamic shape
than near the tip, where most thrust is generated.

I flew the 0-2 in VN. Single engine performance, either front or rear,
was not very good. That being said, the rear engine gave better SE
performance. We were told in ground school that the rear prop sucked
air over the wing center section at a higher velocity and gave more
lift than the front engine could push it up and over the center of
wing.

No matter the reason, the bird flew better SE on rear engine. SE on
either engine, the machine turned into a donut making device or worse
if you were not careful.

Big John
****************************************888

On Sun, 5 Aug 2007 22:15:55 -0400, "Kyle Boatright"
wrote:


"Kingfish" wrote in message
roups.com...
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

The single engine climb performance is pitiful regardless of which engine is
caged, but the aircraft has more performance on the back engine than the
front. That may or may not be due to prop efficiency. It could also be due
to reduced fuselage drag. The tractor prop blows a high speed stream of air
across the fuselage, creating its own source of drag. This isn't as much of
a factor with the pusher.

KB

I would have thought the gain for the rear engine was because the air
stream was not hitting the windscreen and losing energy that way. The
air coming into the prop comes from all directions (just flowing into
a low pressure area) but the stream leaving is directed.

But if in the newer Skymasters both engines give the same single
engine performance my idea has to be wrong






On Aug 9, 2:28 pm, Big John wrote:
I flew the 0-2 in VN. Single engine performance, either front or rear,
was not very good. That being said, the rear engine gave better SE
performance. We were told in ground school that the rear prop sucked
air over the wing center section at a higher velocity and gave more
lift than the front engine could push it up and over the center of
wing.

No matter the reason, the bird flew better SE on rear engine. SE on
either engine, the machine turned into a donut making device or worse
if you were not careful.

Big John
****************************************888

On Sun, 5 Aug 2007 22:15:55 -0400, "Kyle Boatright"



wrote:

"Kingfish" wrote in message
roups.com...
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

The single engine climb performance is pitiful regardless of which engine is
caged, but the aircraft has more performance on the back engine than the
front. That may or may not be due to prop efficiency. It could also be due
to reduced fuselage drag. The tractor prop blows a high speed stream of air
across the fuselage, creating its own source of drag. This isn't as much of
a factor with the pusher.

KB- Hide quoted text -

- Show quoted text -